Within the semiconductor industry, an ever present need exists for improved process repeatability and control. As new generations of integrated circuits employ smaller feature sizes than were contemplated in previous generations, greater demands are placed on the integrated circuit fabrication process. Deposition and etching of one or more layers on a semiconductor substrate in a plasma environment are two of the most common steps in integrated circuit manufacturing. In addition plasma assisted doping (by implantation of species or incorporation of species are being used extensively in the transistor fabrication. Considering that many discrete plasma processing chambers are employed in either the same manufacturing facility or different manufacturing facilities to manufacture products intended to have the same properties, it is very important that a consistent result is produced from one chamber to another chamber either in the same facility or a different facility. Therefore, to ensure that a consistent film is deposited or etched on the substrate, it is important to make sure that the various plasma processing chambers operate substantially in the same manner.
To ensure that a correct amount and quality of film is deposited, etched, implanted or incorporated, a production process chamber needs to be calibrated against a “reference” chamber (which may also be referred to as a “good” chamber or “golden” chamber). The procedure used to compare chambers is sometimes called chamber qualification. Chamber qualification procedures are used at various times during a chamber's use. When a process chamber is newly manufactured, the chamber must be qualified. The new chamber is typically matched to a “golden” chamber to ensure the new chamber will perform according to its specification. Once the chamber is qualified, the chamber can then be shipped to a semiconductor manufacturing facility. Once the chamber arrives at the semiconductor manufacturing facility, the chamber is reassembled and “qualified” again prior to processing the production materials. In addition, production chambers must undergo regular maintenance or cleaning. After maintenance or chamber cleaning, the chamber needs to be “qualified” again prior to running production wafers. Stringent chamber matching techniques that utilize comprehensive plasma monitoring are needed to ensure process repeatability and control in semiconductor manufacturing.
To ensure that a consistent substrate processing occurs in different chambers, each plasma processing chamber is typically matched to a reference “golden” chamber. The plasma state of the chamber during processing needs to match that of a selected process in a “reference” chamber to ensure the chamber and process are functioning as expected. If the plasma state of the process chamber does not match that of a selected “reference” chamber, the processing parameters can be modified to obtain a matching plasma state, resulting in equivalent products.
Besides chamber matching, monitoring a single chamber over a period of time will decrease chamber downtime. By monitoring the plasma state, the operator can predict when a process will result in product which is outside of the acceptable ranges. This will allow for the determination of when preventative maintenance must be performed on the plasma chamber prior to generating products which do not meet the acceptance criteria.
During a plasma process, certain plasma “attributes”, such as the plasma's electromagnetic emissions, the RF power delivered to a wafer pedestal, wafer reflectance, process pressure and process temperature, manifest low frequency fluctuations that contain significant information about the plasma process and the plasma chamber. These attributes affect the resultant process, thereby giving different substrates different surface characteristics. The intensity of a plasma's optical emission spectra (OES) during plasma processing contains information related to the process state, process event and process chamber. OES states are affected to different degrees by varying chamber conditions and by process parameter changes.
While certain methods exist for monitoring process chambers and matching process chamber performance, there is a need for techniques to more accurately match substrate processing chambers to a reference substrate process chamber. There is also a need to more accurately monitor the short- and long-term stability of a plasma processing chamber.